Sepioteuthis lessoniana is a widely distributed neritic squid in the Indo-Pacific Ocean. It is an important species in fisheries, but species management is difficult because of inadequate information regarding its life history. The daily growth and δ 18 O values from the core to the edge of statoliths of S. lessoniana collected in northern Taiwan were analyzed to predict the experienced temperature history along with ontogenetic stages. The probability of occurrence in a given area at each life stage in three seasonal groups was determined using salinity values, deduced and measured temperatures, and the known ecology of S. lessoniana. The results showed that ontogenetic variation in the statolith δ 18 O values in S. lessoniana reflected the seasonal temperature fluctuation observed in Taiwanese waters, which indicated the reliability of the prediction method. Complex and diverse distribution and movement patterns were observed in the three seasonal groups. The results also indicated the importance of the waters near the coast of northeastern Taiwan as a spawning ground. Based on a model prediction, the distribution of S. lessoniana is likely associated with water temperature and current. A potential migration route from the Penghu Islands to northeastern Taiwan suggests a high level of population connectivity in S. lessoniana in Taiwan. This study provides information on the spatial and vertical distribution of S. lessoniana at various ontogenetic stages, which is essential for resource management and conservation of this commercial species.

Temperature histories are critical for understanding and predicting ecological functioning in marine systems. Stable oxygen isotopes (δ18O) locked within calcified tissues can uncover experienced temperatures of marine animals, but have been little evaluated in the statoliths of cephalopods. As such, we investigated field applications of oxygen isotope ratios in statoliths (δ18Ostatoliths) for reconstructing the thermal histories of cuttlefish, octopus, and squid. In doing so, we collated measured (instrumental and modelled) temperature and salinity data, alongside δ18Ostatoliths data, of ocean-caught species from Taiwan and Australia. To navigate potential species-bias or “vital effects,” two aragonite-specific thermometry equations were compared, whilst simulation modelling evaluated variation and addressed uncertainties. Linear regressions identified environmental and biological influences on the differences between measured and reconstructed temperatures. Variable trends in temperature reconstructions were observed between taxa, which may be due to ecological traits. For squid, the relationship was highly aligned with no significant model predictors. For cuttlefish and octopus, differences between measured and reconstructed temperatures increased in warmer conditions, and may indicate thermoregulation behaviour. Here, we demonstrate that δ18Ostatoliths values can function as natural proxies of ocean temperature and are an invaluable tool for broadening the field of thermal ecology for the important, yet understudied, cephalopods.

The use of mass-marking techniques of enriched stable isotopes has increased in studies of ecology, movement patterns and the dispersal of marine organisms. However, the efficacy of this technique and its potential effects on hatchling size and statolith chemistry of cephalopods are yet to be investigated. Sepioteuthis lessoniana egg capsules were collected from northern Taiwan and assigned randomly to 137Ba-spiking experimental groups at 0.2, 0.5 and 1ppm and three immersion durations (1, 3 and 7 days). Immersion duration >3 days produced significantly lower 138Ba:137Ba ratios, with 100% marking success, indicating that it is a reliable marking technique. The 137Ba mass marking had a positive effect on size at hatch and was likely to affect statolith trace element incorporation, including Cu, Zn and Pb. These findings highlight that it is necessary to consider the species-specific effects on hatchling size and physiological responses in when using stable isotopes mass-marking techniques.